Background of the invention
Field of the invention
[0001] This invention relates to an apparatus for controlling the supply of fuel to an internal
combustion engine. More particularly, it relates to an apparatus which can control
the supply of fuel appropriately in the idling or low load condition of the engine
to control the rotation of the engine to a demanded speed when a control valve provided
in a bypass passage for a throttle valve has become in an uncontrollable condition
in the open position and is incapable of controlling the amount of air being introduced
into the engine. This results in an idling speed which is so high that the vehicle
in which the engine is installed cannot be driven properly.
Description of the prior art
[0002] Control valves have been provided in a bypass passage extending between the upstream
and downstream areas of a throttle valve in an air intake for an internal combustion
engine, for controlling the amount of the air being introduced into the engine to
thereby control the engine speed at a constant speed during its idling, i.e., when
it is driven with the throttle valve maintained substantially in a closed position.
[0003] The degree of opening of the control valve is controlled during the idling of the
engine in accordance with the amount of any external load required for an air conditioner,
or the like, in order to ensure an appropriate supply of air to the engine and correspondingly
appropriate supply of fuel so that the engine may produce an appropriate output.
[0004] Further, a fuel cutting system has been provided which reduces the supply of fuel
when it is driven in a decelerating condition, in order to improve the fuel consumption.
[0005] The system functions to cut fuel, for example, when pressure on the accelerator has
been released, resulting in substantially the complete closure of a throttle valve.
The fuel cutting system ceases to function when the rotating speed of the engine has
been reduced to a predetermined engine speed which is slightly higher than the idling
speed.
[0006] When the engine speed continues to be maintained around the predetermined engine
speed in a particular driving condition, the fuel cutting system repeatedly operates
by turning on and off, and the operator repeatedly feels sudden changes of engine
torque. Hitherto, in order to avoid the changes, the fuel cutting system has a hysteresis
area between the engine speeds which stops and starts fuel cutting.
[0007] In order to prevent the hunting of the engine, it has hitherto been usual to raise
the rotating speed of the engine at which the fuel cutting system functions and lower
the rotating speed at which the system ceases to function. Therefore, the conventional
fuel cutting system functions to cut the supply of fuel to reduce the engine speed
in an area which is shown by broken lines in Figure 5. It contains a hysteresis area.
[0008] The prior art as hereinabove described has the following problems:
(1) In the event an excessive increase in the amount of air being introduced into
the engine during its idling has resulted from, for example, the failure of the control
valve or a circuit for driving it, the engine is likely to have an increased rotating
speed, as fuel is supplied in an increased quantity corresponding to the amount of
the air.
Therefore, the engine is likely to hunt heavily around the hysteresis area of the
fuel cut area. If the accelerator is pressed to start the vehicle, the fuel cutting
system ceases to function and as a result, it is likely that the rotating speed of
the engine will increase suddenly, or that the vehicle may start or be accelerated
suddenly if the power of the engine is transmitted to the driving wheels (i.e., when
the vehicle is in gear).
(2) There is also known a device for detecting any excessive reduction in the amount
of the air being introduced into the engine during idling as a result of, for example,
the failure of the control valve or the circuit for driving it, and keeping all the
valves fully open to increase the amount of the air to avoid engine stall.
[0009] In this case, however, the fuel is supplied in an increased quantity corresponding
to the amount of the air and the idling of the engine has an increased rotating speed.
As a result, there arises the same problems as those stated in (1) above.
[0010] In "L-Jetronic, Bosch", April 1981, pages 6, 7 and 14 to 17 there is disclosed an
apparatus for controlling the idle fuel supply of an internal combustion engine having
a control valve means for controlling the amount of air to be supplied to an engine
piston downstream of a throttle valve; the apparatus comprising:
an engine speed sensor for detecting the rotating speed of the engine;
a throttle opening sensor for detecting the degree of opening of the throttle valve;
and
[0011] fuel cut means coupled to the engine speed sensor and the throttle opening sensor
for determining a fuel cut area free from hysteresis and that is defined by the degree
of throttle opening and the rotating speed of the engine, and for executing fuel cut
in response to the output of the engine speed sensor and the throttle opening sensor
indicating that the engine is operating within the fuel cut area. In this apparatus
there is no provision for detecting disorder in the amount of air supplied to the
engine piston. Disorder detecting means are disclosed in DE-A-3 322 240 (see the abstract
and claim 1), GB-A-2 142 171 (see Figure 1 and the abstract) and GB-A-2 127 585 (see
Figure 1, Figure 5 for example steps 1 and 10, page 5 lines 43 to 100).
[0012] According to the present invention there is provided an apparatus for controlling
the idle fuel supply of an internal combustion engine having a control valve means
for controlling the amount of air to be supplied to an engine piston downstream of
a throttle valve; the apparatus comprising:
an engine speed sensor for detecting the rotating speed of the engine;
a throttle opening sensor for detecting the degree of opening of the throttle valve;
and
fuel cut means coupled to the engine speed sensor and the throttle opening sensor
for determining a fuel cut area free from hysteresis and that is defined by the degree
of throttle opening and the rotating speed of the engine, and for executing fuel cut
in response to the output of the engine speed sensor and the throttle opening sensor
indicating that the engine is operating within the fuel cut area;
characterised in that the apparatus further comprises means for detecting disorder
in the amount of air supplied to the engine piston and outputting a disorder indicating
signal;
in that the fuel cut means is also coupled to the disorder detecting means for determining
the fuel cut area in response to a disorder indicating signal when the outputs of
the engine speed sensor and the throttle opening sensor indicate that the engine is
operating within the fuel cut area;
and in that the fuel cut area is defined such that the rotating speed of the engine
at which the supply of fuel is cut increases linearly with an increase in the degree
of throttle opening. Because, in this apparatus, the fuel cut area is such that the
rotating speed of the engine at which the supply fuel is cut increases linearly with
an increase in the degree of throttle opening, there is no possibility of the engine
having a suddenly increased rotating speed, or the vehicle starting or being accelerated
suddenly, even if the accelerator is pressed when the throttle valve is substantially
in its fully closed position. In addition, even if there is a failure of, for example,
the control valve or the circuit for driving it which causes an excessive increase
in the amount of the air being introduced into the engine during idling, or an excessive
decrease in the amount of air which results in the opening of all the valves and eventually
the supply of an excessive amount of air to the engine, the supply of fuel is cut
if the rotating speed of the engine exceeds a predetermined level. Therefore, there
is no idling of the engine at a speed exceeding a predetermined level.
[0013] For a better understanding of the invention, and to show how the same may be carried
into effect, reference will now be made, by way of example, to the accompanying drawings,
in which:
Figure 1 is a block diagram showing the operation of apparatus for controlling the
idle fuel supply of an internal combustion engine,
Figure 2 is a schematic representation of a preferred embodiment of such apparatus,
Figure 3 is a circuit diagram of an electronic controller of the apparatus of Figure
2,
Figure 4 is a flow chart showing the operation of a microcomputer of the apparatus,
and
Figure 5 shows a fuel cut decision table stored in the ROM of a memory device of the
controller of Figure 3 which defines a predetermined fuel cut area.
Detailed description of the preferred embodiment
[0014] The preferred embodiment of the invention will now be described in further detail
with reference to the drawings.
[0015] Figure 2 is a diagrammatic representation of an apparatus embodying the present invention.
If a throttle valve 32 is brought to a substantially fully closed position (for example,
to an angle of, say, less than 3° to 5°, which will hereinafter be called the idling
angle of opening), the amount of air being introduced through an intake manifold 33
is controlled by a control valve 30 provided in a bypass passage 31 extending between
the upstream and downstream areas of the throttle valve 32. The opening degree of
the control valve 30 depends on the amount of electric current supplied to a linear
solenoid 16.
[0016] The amount of fuel which is injected through an injection nozzle 34 is determined
by a known injector device in accordance with the amount of air being introduced through
the intake manifold 33. A piston 38 in a cylinder 35 repeats reciprocal motion and
imparts a rotating force to a crankshaft 36.
[0017] An engine speed sensor 2 detects the rotating speed of the engine by an appropriate
method and supplues a digital signal to an electronic controller 40. A throttle opening
sensor 39 supplies a digital signal indicating the opening degree of the throttle
valve 32 to the electronic controller 40.
[0018] The electronic controller 40 controls the electric current to the linear solenoid
16, as will hereinafter be described in further detail, and also determines if the
degree of throttle opening and the rotating speed of the engine indicate that the
engine is operating within a predetermined fuel cutting area, when the amount of the
air being introduced into the engine is uncontrollable. If the results of the determination
are positive, the controller generates an output signal commanding a fuel cut.
[0019] Figure 3 is a circuit diagram showing the construction of the electronic controller
40. Like numerals are used to designate like or equivalent parts in both of Figures
2 and 3.
[0020] The electronic controller 40 comprises a microcomputer 53 and a driving circuit 54.
The microprocessor 53 includes a central processing unit (CPU) 50, a memory 51 and
an input and output signal processing circuit (interface) 52. The driving circuit
54 is, for example, adapted for controlling the electric current to the linear solenoid
16 in accordance with the output of the microcomputer 53.
[0021] According to the arrangement shown in Figure 3, one end of the linear solenoid 16
is connected to the driving circuit 54, and the other thereof is connected to a battery
55. Numeral 56 denotes a solenoid for the injection nozzle 34 (Figure 2).
[0022] When the throttle valve 32 (Figure 2) is open at the idling angle to enable the idling
of the engine, a command value I
cmd for the current to be supplied to the linear solenoid, is calculated by the CPU 50
in accordance with the following equation (1) and produced as an output by the interface
52:
where I
fbn is the term of PID feedback control (basic control), i.e., proportional (P), integral
(I), or differential (d) control based on a deviation of the actual rotating speed
of the engine detected by the engine speed sensor 2 from a target idling speed as
a function of engine temperature,
[0023] I
e is the term of correction for adding a predetermined value in accordance with the
load of an AC generator (ACG), i.e., its field current,
[0024] I
at is the term of correction for adding a predetermined value when the selector of an
automatic transmission (AT) is positioned in a drive (D) range,
[0025] I
hac is the term of correction for adding a predetermined value when an air conditioner
is in operation.
[0026] In order for the CPU 50 to calculate I
cmd when all of the terms of equation (1) have been obtained, it is necessary to employ
a number of appropriate sensors in addition to the engine speed sensor 2 and the throttle
opening sensor 39 and to apply the outputs of the sensors to the microcomputer 53.
This is, however, well known and a matter of common knowledge and thus none of the
additional sensors are shown in the drawings.
[0027] The value of I
cmd, calculated in accordance with the equation (1), is fed from the interface 52 to
a variable duty oscillator 57 forming a part of the driving circuit 54. The variable
duty oscillator 57 outputs a pulse signal having a duty ratio controlled in accordance
with l
cmd.
[0028] The output of the variable duty oscillator 57 is applied to the base of a transistor
Tr
1 for driving the linear solenoid. As a result, the transistor Tr
1 is driven in accordance with the output of the oscillator 57.
[0029] According to the arrangement shown in Figure 3, electric current flows from the battery
55 to ground through the linear solenoid 16, the transistor Tr
1 and a resistance R
i, depending on the state of the transistor Tr
i. The electric current (solenoid current) provides the linearcontrol of the opening
degree of the control valve 30 (Figure 2).
[0030] According to the arrangement of Figure 3, the solenoid current is detected as a voltage
drop at the resistance R
1 and is converted by a current detecting circuit 58 to a digital signal which is fed
to the interface 52. In other words, the interface 52 receives a digital signal representing
the amount of electric current I
act which flows through the linear solenoid 16.
[0031] The signal indicating I
act and the output of the engine speed sensor 2 (engine speed signal) enable the microcomputer
53 to determine whether the amount of air being introduced into the engine is uncontrollable,
as will hereinafter be described in further detail.
[0032] If the amount of air has been determined as being uncontrollable, the apparatus determines
whether it is necessary to cut the supply of fuel, based on the actual opening degree
of the throttle valve 32 (throttle opening θ
th) and the rotating speed No of the engine.
[0033] The control of fuel supply will now be described with reference to the drawings.
[0034] Figure 4 is a flow chart illustrating the operation of the microcomputer 53.
[0035] The microcomputer 53 starts its operation for the control of the fuel supply in accordance
with an interrupt signal which is synchronized with the rotating speed of the engine.
[0036] Step S1-Determines whether the state that the electric current I
act is much lower than the minimum value 1
0 of I
cmd (for example, about 200 mA) for a predetermined length of time (for example, three
seconds). If the results of this determination are affirmative, processing proceeds
to Step S5, and if not, it proceeds to Step S2.
[0037] When the result of the determination of Step S1 is affirmative, it is possible that
one of the following events may have occurred in the circuit of Figure 3:
(1) Shortcircuiting to ground of point B in Figure 3;
(2) Breakage at point B;
(3) The transistorTr, remains in its OFF position;
(4) Breakage at point C in Figure 3; or
(5) The current detecting circuit 58 has failed and its output remains at a low level.
[0038] However, even if the affirmative results of the determination Step S1 are due to
cause (1) or (5), an electric current flows to the linear solenoid 16. In the case
of (1), the electric currentwhich flows to the linear solenoid 16 is so large that
the control valve 30 is substantially fully opened. In the case of (5), however, it
is sometimes possible that an appropriate amount of electric current may flow to the
linear solenoid 16 and thereby keep control valve 30 appropriately open.
[0039] When any of the causes (2) to (4) exists, no electric current flows to the linear
solenoid 16, but the control valve 30 remains substantially in its fully closed position.
In such an event, the apparatus of the present invention includes known appropriate
means for fully opening the valves to ensure that an appropriate amount of air is
introduced into the engine.
[0040] Step S2-The microcomputer determines whether the state that the value of I
act is much greater than I
cmd (I
act>>I
cmd) for a predetermined length of time (for example, three seconds). If the results
of its determination are affirmative, the operation proceeds to Step S5, and if not,
it proceeds to Step S3.
[0041] When the results of the determination at Step S2 are affirmative, it is possible
that either of the events (6) and (7) may have occurred in the circuit of Figure 3:
(6) The transistor Tr, remains in its ON position; or
(7) The current detecting circuit 58 has failed and its output remains at a high level.
[0042] Even if the affirmative results of the determination Step S2 are due to the cause
(7), it is sometimes likely that an appropriate amount of electric current may flow
in the linear solenoid 16 and thereby keep the control valve 30 appropriately open.
[0043] Step S3-This step is to determine whether the engine has hunted heavily more than
a predetermined number of times (for example, three times) within a predetermined
length of time (for example, 10 seconds), or not.
[0044] More specifically, the microcomputer considers the output of the engine speed sensor
2 to see if the rotating speed of the engine has shown any variation having an amplitude
wider than a predetermined amplitude, and determinewhetherthe variation has occurred
more than the predetermined number of times within the predetermined length of time.
[0045] If the results of this determination are affirmative, it proceeds to Step S5. If
not, it concludes that there is nothing wrong with the intake system including the
driving circuit 54 for the linear solenoid 16, and proceeds to Step S4.
[0046] When the results of the determination at Step S3 are affirmative, it is likely that
any of the failures (8) to (10) may have occurred:
(8) The control valve 30 is mechanically fixed in a larger opened position than during
its normal operation;
(9) While the throttle valve 32 comprises a primary valve and a secondary valve, the
latter has a mechanical fault which disables it to return properly to its original
position (the degree of throttle opening is typically represented by the degree of
opening of the primary valve); or
(10) Air leaks into the intake manifold 33 due, for example, to the disconnection
of a pipe for measuring the negative pressure prevailing in the intake manifold, or
a pipe in an exhaust gas recirculating (EGR) system.
[0047] If a vehicle is equipped with a fuel cutting system for reducing its speed, hysteresis
arises between the rotating speed of the engine at which the fuel cutting system is
placed out of operation and its rotating speed at which the system is placed from
its inoperative position to its operative position, as hereinbefore stated. Therefore,
the presence of any of the causes (8) to (10) gives rise to the heavy hunting of the
engine.
[0048] Step S4-A fuel cut decision area T
1 which employs the degree of throttle opening 8
th and the rotating speed of the engine N
9 to define a fuel cut area for operation at a reduced speed as inner area of dotted
line in Figure 5, is read from the newest information on the degree of throttle opening
as detected by the throttle opening sensor 39 and the newest information on the rotating
speed of the engine as detected by the engine speed sensor 2. The fuel cut decision
area T
1 is stored in a ROM (read only memory) in the memory 51. If the engine is operating
within the fuel cut area for operation at a reduced speed, the supply of fuel is cut
by a known appropriate device.
[0049] Step S5-A fuel cut decision table T
2, which uses the degree of throttle opening θ
th and the rotating speed of the engine N
e to define a fuel cut area as shown in Figure 5, is read from the newest information
on the degree of throttle opening detected by the throttle opening sensor 39 and the
newest information on the rotating speed of the engine as detected by the engine speed
sensor 2. The fuel cut decision table T
2 is also stored in the ROM of the memory 51.
[0050] The fuel cut area shown by oblique lines in Figure 5 does not contain any hysteresis
portion. Therefore, if the accelerator is not pressed, but the throttle valve 32 is
substantially in its fully closed position (or has an open angle not exceeding 3°
according to the apparatus of this invention as herein described), the fuel cutting
system is activated if the engine has a rotating speed of 1200 rpm or above and its
operation discontinued if the rotating speed of the engine drops below 1200 rpm.
[0051] Accordingly, the rotating speed of the engine is maintained substantially at 1200
rpm. The fuel cut area is such that if the accelerator is pressed on lightly, the
rotating speed of the engine at which the supply of fuel is cut increase linearly
until the throttle valve opens to an angle of 5°. This enables the smooth operation
of the engine even if the intake system has a malfunction.
[0052] The speed of 6800 rpm appearing in Figure 5 is illustrative of the maximum rotating
speed that is mechanically permissible for an internal combustion engine.
[0053] Step S6-This step is to determine from the signal read out at Step S4 or Step S5
whether or not the engine is operating within the fuel cut area shown in Figure 5.
If the results of the determination are affirmative, the operation proceeds to Step
S8, and if not, it proceeds to Step S7.
[0054] Step 57-This step is to discontinue the outputting of a fuel cut command signal at
Step S8 which will hereinafter be described. Then, the operation returns to the main
program, and in main program fuel is supplied into the cylinder.
[0055] Step S8-The microcomputer produces a fuel cut command signal as an output. As a result,
the supply of fuel is cut in response to the fuel cut command signal. Then the operation
returns to the main program.
[0056] Referring now to Figure 1, which is a block diagram showing the operation of the
apparatus according to this invention, an Imd producing device 101 produces an I
cme signal after calculation in accordance with, for example, equation (1). An electric
current control device 102 is driven in response to the I
cmd signal to control the amount of the electric current flowing to the linear solenoid
16. An I
act detecting device 103 detects the amount of electric current l
act which flows through the linear solenoid 16.
[0057] An I
act<<I
o or l
act«lcm
d device 104 compares the values of I
act and I
cmd and determines whether the state that I
act is much lower than 1
0 (I
0 being the minimum value of Icmd as hereinbefore stated), or much higher than I
cmd, has lasted for a predetermined length of time, or not.
[0058] If the results of the determination are affirmative, the device 104 feeds a disorder
indicating signal (having a logic value of "1") to one of the terminals of an OR gate
105a.
[0059] A hunting detecting device 106 receives the output of the engine speed sensor 2 and
determines whether the engine has hunted heavily more than a predetermined number
of times within a predetermined length of time. If it has detected any such hunting,
it feeds a disorder indicating signal (having a logic value of "1") to the other terminal
of the OR gate 105a.
[0060] The OR gate 105a outputs a "1" signal when it has received an output signal from
either of the devices 104 and 106. The output of the OR gate is held by a resistor
105c and fed to a fuel cut area storing device 107.
[0061] The device 107 stores a fuel cut decision table (such as table T
2) showing the fuel cut area defined by the degree of throttle opening θ
th and the rotating speed of the engine N
e.
[0062] When it has received the "1" signal from the resistor 105c, the device 107 outputs
a fuel cut command signal (having a logic value of "1") if the degree of throttle
opening and the rotating speed of the engine indicate that the engine is operating
within the fuel cut area.
Advantages of the invention:
[0063] As is obvious from the foregoing description, this invention provides the following
advantages:
(1) Even if there is a failure of, for example, the control valve or the circuit for
driving it which causes an excessive increase in the amount of the air being introduced
into the engine during idling, or an excessive decrease in the amount of air which
results in the opening of all the valves and eventually the supply of an excessive
amount of air to the engine, the supply of fuel is cut if the rotating speed of the
engine exceeds a predetermined level. Therefore, there is no idling of the engine
at a speed exceeding a predetermined level.
[0064] The fuel cut area is such that the rotating speed of the engine at which the supply
fuel is cut increases linearly with an increase in the degree of throttle opening.
Therefore, there is no possibility of the engine having a suddenly increased rotating
speed, or the vehicle starting or being accelerated suddenly, even if the accelerator
is pressed from when the throttle valve is substantially in its fully closed position.
(2) The fuel cut area according to this invention is free from any hysteresis, as
opposed to the prior art. Therefore, there is no heavy hunting of the engine.
[0065] Thus, the apparatus of the present invention improves the riding comfort of a vehicle
and the ease of driving as compared to a vehicle equipped with a conventional fuel
cutting system, when the amount of air being introduced into the internal combustion
engine is uncontrollable.